The present invention relates to an improvement in steam turbines and especially to a pressure seal ring anti-wedging relief groove in a throttling valve.
Electric utility power generating systems generally comprise an alternating current electric power generator driven by a turbine. While some systems employ water turbines, most systems utilize steam turbines in which a controlled steam flow through the turbine regulates the rotational velocity of a driven turbine shaft. The steam flow is controlled, in response to electric power demands placed on the generator, such that the frequency of the alternating current produced by the generator is maintained at a constant value regardless of variations in electric power demands placed on the generator. The steam flow in turn is controlled by various flow control valves such as throttling valves and steam bypass valves.
The present invention relates to an improvement in the flow control valves of a steam turbine and especially to a throttling valve. In the past, these valves had a valve plug riding in a bonnet cylinder with the valve plug having one or more pressure seal ring grooves therein. A pressure seal ring can maintain the pressure drop across the ring which results in the pressure seal ring contacting the valve plug. In service, it has been found that the pressure seal ring wears a step in the contact surface along the edge of pressure seal ring groove of the valve plug. The resultant step worn along the edge of the groove can result in a wedging of the pressure seal ring between the valve plug and the bonnet cylinder bore and the resultant inability of the valve to close as required for turbine overspeed protection. The aim of the present invention is to prevent this wedging of the pressure seal ring between the valve plug and the bonnet cylinder bore as the pressure seal wears into the groove wall of the valve plug.
Typical throttling valves and steam bypass valves can be seen in prior U.S. Pats. to Heymann for a Noise Suppressing Throttle Valve, No. 3,857,542, and in the Brown et al. U.S. Pat. No. 3,602,261, for a Steam Turbine Control Valve Structure and in the Dawawala et al. Pat. No. 4,679,769, for a Steam Turbine Control Valve for Cyclical Duty. This latter patent shows an overall configuration of a one-piece bonnet control valve. These patents are all assigned to Westinghouse Electric Corporation.